A switchable optical device such as an electrochromic device reversibly cycles between two or more optical states such as a clear state and a colored state. Switching between these states is controlled by applying predefined current and/or voltage to the device. The device controller typically includes a low voltage electrical source and may be configured to operate in conjunction with radiant and other environmental sensors, although these are not required. The controller may also be configured to interface with an energy management system, such as a computer system that controls the switchable optical device according to factors such as the time of year, time of day, security conditions, and measured environmental conditions. Such an energy management system can dramatically lower the energy consumption of a building, reduce glare, and maximize day lighting.
While electrochromic devices and related optically switchable devices were invented decades ago, they have not begun to realize their full commercial potential. Part of the difficulty is a lack of versatility in the operating modes of electrochromic devices. Additionally, known control systems for electrochromic devices have limited functionality and fail to account for some of the unique features of electrochromic devices, as well as user preferences.